Water heating in residential and commercial establishments has been carried out for many years by providing a burner below a tank of water controlled by a thermostat. In the past, the efficiency of such domestic water heaters was of little concern as natural gas and bottled gas used as an energy source were relatively inexpensive.
The content of the exhaust gases of such water heaters was also of little concern. The gas burned was considered a clean fuel and each installation was so small that products of combustion introduced into the atmosphere by such units were ignored.
The efficiency of all gas consuming appliances has now become more of a concern to both government units and the public at large. Also, the products of combustion of gas have come under government scrutiny, and in some jurisdictions, the amount of certain gases produced by domestic gas water heaters is now the subject of regulation.
Oxides of nitrogen generated by the combustion of fuels are currently the subject of governmental interest and regulation. Oxides of nitrogen are believed to react in the atmosphere to form ozone. Oxides of nitrogen are also believed to react with hydrocarbon pollutants in a complex manner to form chemicals which irritate the eyes and nose and may be harmful. Because of this, emissions of oxides of nitrogen from many sources including water heaters are regulated in the Los Angeles area. Regulation of emission of oxides of nitrogen is becoming more widespread.
Attempts have been made in the past to address the efficiency issue in domestic gas water heaters. U.S. Pat. No. 4,397,296 to Moore, et al., describes a water heater using a combustion chamber surrounded by a body of water to be heated. Such an arrangement minimizes heat loss to the atmosphere from the combustion chamber thereby improving efficiency. While this structure improves efficiency, it increases the cost of manufacturing the water heater because of the complex construction involved.
U.S. Pat. No. 4,301,772 to Eising also proposes to increase efficiency by disposing a combustion chamber within the body of water to be heated. This structure uses a cylindrical combustion chamber inclined with respect to horizontal. Means are provided to deal with water condensed from the products of combustion which gather in this inclined combustion chamber and flow toward the burner opening.
Neither of these patents discusses the reduction of oxides of nitrogen in the products of combustion.